Elastic fluid turbine bucket wheel



Nov. 12, 1940.

A. R. SMITH ELASTIC FLUID TURBINE BUCKET WHEEL Filed Aug. 27, 1938 Inventor. Arthur F2. Smith. b5 7 E49 His Attorngg.

Patented Nov. 12,

PATENT orrlcs 2,220,918 ELASTIC FLUID TURBINE BUCKET wnu Arthur a smah, Schenectady, N. r., assignor to General Electric Company, a corporation of New- York Application August 27, 1938, Serial No. 227,152

- 3 Claims.

The present invention relates to elastic fluid turbine bucket wheels'and more particularly to arrangements for securing the buckets against movement on the rim of the wheel.

5 In axial flow elastic fluid turbines, the buckets are frequently secured onto the rim of the wheel disk by a dovetail connection; In the manufacture of the cooperating dovetail portions, it is difiicult and often impracticable to attempt to .10 provide an absolutely tight fit between the individual bucket bases and the rim. In the operationof the turbine; the elastic fluid emerging from the nozzles exerts its force substantially tangentially of the wheel against the buckets. Due to the'relative narrowness of the bucket bases and, depending upon factors including the closeness of the fit "in the dovetail connection, the buckets are caused to rock slightly'on the rim under each impulse of operating fluid. The repeated rocking of the buckets, which is particularly pronounced in high pressure partial admission type turbines, together with the peripheral bending of the loaded buckets, results in the severe stressing of the cover tie band or of the attaching tenons and may cause fatigue of such parts and their consequent failure.

It is an object of the present invention to provide a new and improvedarrangement for interlocking turbine buckets of the type described whereby peripheral deflections of the buckets from the radial position are minimized.

It is a further object of the invention to provide a new and improved arrangement of buckets whereby the bases of adjacent buckets are interlocked so that the effective base width of the individual buckets is increased and whereby they are held substantially immovable with respect to' I the rimand capable of withstanding severe operating conditions.

40 For consideration of what I believe to benovel and my invention, attention is directed to the following description and the claims appended thereto taken in connection with the accompanying drawing. l

In the drawing, Fig.1 is a perspective sectional view of a portion of a bucket wheel provided with buckets according to my invention; Fig. 2 is a perspective sectional view of a portion of a bucket wheel provided with buckets according to a modifled form of my invention; while Fig. 3 is a fragmentary cross-sectional elevation illustrating certain details in connection with the secondmodification.

Referring to Fig. 1 of the drawing, Ill indicates the web of the wheel or rotor and I l the grooved rim which on opposite sides is provided with annular shoulders defining a dovetailed portion I! for retaining the buckets l3 thereon. The bucket bases l4 are provided with a grooved slot defining an inverted dovetail for cooperatively fit- 5' ting over the rim of the wheel substantially as shown. The buckets are assembled on the rim in the usual manner, one or more" filling slots (not shown) being provided in the rimas is welli understood. The bucket fastening means de- 10 scribed forms what is commonly termed the inverted dovetail type of fastening and in itself is well-known in the art. It may be taken as typical of a suitable type of fastening'in connection with which my invention may be carried out.

It is the usual practice-to allow a certain clearance between the wheel rim dovetail and the dovetail slot in the bucket bases so that the buckets, after insertion through the filling slots, may be slid around the periphery of the rim into position. This clearance, even though slight,'will allow considerable rocking of the buokets in the radial plane when subjectedto the force of the operating fluid because of the. relative narrowness of the individual bucket bases. It isunderstood that the rocking movements of the individual buckets are accompanied by a relative sliding movement between the abutting faces of the bucket bases. By suitably interlocking the faces of the adjacent bases relative movement 30 therebetween is precluded and the buckets are maintained substantially rigid on the rim. Ac: cording to my invention, I provide the abutting faces of the bucket bases with cooperating tongues l5 and grooves 16 which, while shown as being rectangular in configuration, may be of any other suitable design. The tongues and grooves extend laterally across the faces of the bucket bases or, in other words, substantially perpendicularlywith respect to the plane of the wheel disk. Any suitable number of tongues and grooves may be provided distributed over the length of the abutting faces including the dovetail rootportions, as

. shown. The tongues and grooves on opposite of the adjacent buckets are provided on their abutting faces with cooperating tongues l8 and grooves l9 similar to the tongues I and grooves it provided on the base portions. As the buckets are assembled on the rim, the cover portions '20, 20' and 2| of the ad'j acent buckets fit together to form a. substantially continuous cover extending around the periphery of the wheel. Due to the interlock-'; ing tongues and grooves of the cover portions, relative longitudinal sliding movements therebetween are substantially precluded and consequently peripheral bending deflections of the individual buckets are effectually resisted. By properly dimensioning the proportions of the cover portions, the bucket assembly may be-s0 stiffened as to substantially preclude bending thereof under load.,

In the modification of the invention illustrated in Fig. 2, the abutting faces of the bucket bases and the integral cover portions are provided with aligned recesses or grooves 20 and 2| respectively. These recesses, as in the case of the tongues andgrooves of the previous modifications, extend laterally across the abutting faces, or in other words, substantially perpendicularly with respect to the plane of the wheel disk. After the buckets are assembled onto the rim .of the wheel, suitable keys or pins 22 and 23 are inserted into the aligned recesses 20 and 2| respectively and secured therein as by riveting the ends as indicated at 24 and 25. The pins 22 may be secured in the aligned recesses 20' provided in the base roots as by peening over the outer edges of the recesses as indicated at 26 in Fig. 3.

To insure that the various recesses, or grooves in. the abutting faces will be in perfect alignment, it is preferred to assemble the buckets on the rim without first providing the recesses in the abutting faces. After the buckets are assembled upon the wheel and clamped securely in position, holes may be drilled in the plane of the engaging faces. The semicylindrical recesses thus provided in each of the abutting faces will inherently be in perfect alignment with each other. The various pins may then be inserted and riveted in position rigidly interlocking the bucket assembly.

The manufacture of buckets according to my invention is considerably facilitated by the fact that the axial or abutting faces of the bucket covers are plane and located in substantially the same radial planes as the'corresponding abutting faces of the bases. The axial widths of the bases are about equal to the axial widths of the cov- -ers.- From another viewpoint, the cylindrical projections of the covers onto the bases coincide with the contours of the latter. This is'indicated by dash-dottedlines 21 on the right-hand part of Fig. 1. The last bucket shown in this figure has axial plane surfaces located in the same radial planes as the corresponding axial plane surfaces of the bucket base. with such an arrangement the faces of the cover may be easily machined in the same operation with the machining of the faces of the base. By face I mean the surface of a. bucket which faces or abutsa corresponding surface or face of another bucket. On one side the faces of the base and the cover from axial grooves which when assembled define part of a connection with an adjacent bucket. In the arrangement of Fig. 1 thethe invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the'United States, is:

1. An elastic fluid turbine bucket wheel having a disk with a rim and a row of buckets secured to the disk, each bucket having a base, a blade extending radially from the base and hav-'- ing an end integral therewith and a cover intee gral with the other end of he blade, the base and the cover having plane faces and corresponding faces of the base and the cover being located in substantially the same radial planes, and interlocking means including recesses formed in the faces and intermediate projections cooperatin therewith for securing adjacent buckets together.

2. An elastic fluid turbine bucket wheel havin a, disk with a rim and a row of buckets secured to the disk, each-bucket having a base, a blade extending radially from the base and having an end integral therewith and a cover'integral with the other end of the blade, the base and cover having'piane faces and corresponding faces of the base and the cover being located in substan-.

. tially the same radial planes and provided with axial recesses located so as to register with corresponding recesses'in the faces of adjacent buckets, and axial pins adapted to be received in the v apertures formed by said corresponding recesses to provide an interlocking connection between said buckets.

3. A bucket for axial flow elastic fluid turbine wheels comprising a dovetailed base, a cover, a. blade having ends integrally formed with the base and the cover respectively, the cylindrical projectionof the cover onto the base coinciding with the contour of the latter, the base and the cover having plane faces, the faces of the base and the cover on one side of the bucket each forming "a groove and on the other side a tongue for connection with the tongues and grooves re.- spectively formed by. adjacent buckets.-

v "ARTHURRSMITH. 

